views: Target the synthetic wheel events to the view under the mouse cursor.

ui/views/widget/root_view.cc

Index: ui/views/widget/root_view.cc
diff --git a/ui/views/widget/root_view.cc b/ui/views/widget/root_view.cc
index 5b0de0bc65ef63f85f4f593c24587890e4543990..12c2d12cbb37feb7b0a530af2899544f72ae886e 100644
--- a/ui/views/widget/root_view.cc
+++ b/ui/views/widget/root_view.cc
@@ -139,6 +139,30 @@ void RootView::DispatchScrollEvent(ui::ScrollEvent* event) {
        v && v != this && !event->stopped_propagation(); v = v->parent()) {
     v->OnScrollEvent(event);
   }
+
+  if (event->handled() || event->type() != ui::ET_SCROLL)
+    return;
+
+  // Convert unprocessed scroll events into mouse-wheel events. Note that
+  // wheel events are normally sent to the focused view. However, if the focused
+  // view does not process these wheel events, then dispatch them to the view
+  // under the cursor.
+  ui::MouseWheelEvent wheel(*event);
+  if (OnMouseWheel(wheel)) {
+    event->SetHandled();
+  } else {
+    View* focused_view =
+        GetFocusManager() ? GetFocusManager()->GetFocusedView() : NULL;
+    View* v = GetEventHandlerForPoint(wheel.location());
+    if (v != focused_view) {
+      for (; v && v != this; v = v->parent()) {
+        if (v->OnMouseWheel(wheel)) {
+          event->SetHandled();
+          break;
+        }
+      }
+    }
+  }
 }
 
 void RootView::DispatchTouchEvent(ui::TouchEvent* event) {